“One of my favorite studies found that if you memorize sets of positive, neutral, and negative words, then sleep for seven to eight hours, you will remember around 80 percent of all three lists a day later. If you miss a night of sleep and stay up for thirty-six hours as I did, you still remember most of the negative and neutral words, but you remember 59 percent fewer positive words!20 This is because your brain interprets a lack of sleep as a threat to the central nervous system, then goes on high alert, scanning the world for additional threats—that is, negatives.”